Geologists take very thin slices of rock and look at them under a microscope
to see what minerals make up the rock. This is a photograph taken through
a microscope of the interior of a seafloor lava. The large white crystals
(red arrow) and the tiny white needles are a mineral called plagioclase. The
yellow and green crystals are a mineral called olivine (yellow arrow). The
highly colored regions between the plagioclase crystals are another mineral
called pyroxene. The dark background is glass that has not been fully crystallized.